Residual stress in laser cladded rail

To improve the fatigue life of components subject to loads with high surface strain gradients, it is possible to coat them with an alloy of higher durability. The present study focuses on the effect of cladding high value track components, made of a standard rail steel UIC 900A/grade 260, with a layer of a premium martensitic stainless steel to reduce wear and fatigue. The laser cladding process inevitably generates residual stresses in the clad and parent metal, which could be detrimental to the integrity of the component. Therefore, measurements to determine the residual stress state of cladded rail were performed using semi-destructive centre-hole and deep hole drilling and non-destructive neutron diffraction techniques. Subsequently, the effects of cycling loading and wear, representative of typical service loads, on the redistribution of the residual stress field were investigated. It was observed that laser cladding causes a triaxial compressive residual stress field in the clad and near the interface and a tensile stress field in the parent material. The stress field is shown to change when the first cycle of load is applied but reaches a steady state after only 10 cycles: After the 10th cycle there is no evidence that the clad continues accumulating strain which could indicate that there is low risk of ratcheting. Wear effect on residual stress redistribution was found to be local on the surface of the specimen only

In situ neutron diffraction measurement of residual stress relaxation in a welded steel pipe during heat treatment

Many previous studies have presented results on the relaxation of residual stress in a welded component as a result of postweld heat treatment. Techniques such as neutron diffraction and deep hole drilling have been used to measure the residual stress after the heat treatment and compare this with the residual stress for the component in the as-welded condition. The work described in this paper is novel: neutron diffraction is used to measure the relaxation of residual stress continuously as the heat treatment is being carried out. Residual stresses are measured in a butt-welded ferritic steel pipe as the pipe is heat treated to 650 °C and then cooled to room temperature. The results identify those parts of the heat treatment that lead to significant stress relaxation and the mechanisms responsible for this relaxation. The techniques developed during this work allow future heat treatm